The Organization of the Petroleum Exporting Countries pumped 28.40 million barrels per day last month, down 100,000 bpd from November's revised total, the survey showed, with Iran posting the largest decline.
OPEC+, comprising OPEC and allies including Russia, has slowed the pace of its monthly output increases amid concerns of a supply glut. Many members are running limits and some are tasked with extra cuts to compensate for earlier overproduction, limiting the impact of further increases.
Under an agreement by eight OPEC+ members covering December output, the five of them that are OPEC members - Algeria, Iraq, Kuwait, Saudi Arabia and the UAE - were to raise output by 85,000 bpd before the effect of compensation cuts totalling 135,000 bpd for Iraq and the UAE.
The survey shows that the actual increase by the five was 20,000 bpd.
Iranian crude supply dropped by 100,000 bpd in December, the survey found. Iran is subject to U.S. sanctions that seek to curb its oil exports over Tehran's nuclear work, with the latest measures announced in December. Exports also vary month on month as ships return from making deliveries, tanker trackers say.
Venezuelan crude supply declined by 70,000 bpd in December, the survey found, amid a U.S. blockade to reduce oil shipments, with the impact estimated to increase this month.
Consultant Energy Aspects has not seen a meaningful change to Venezuela's production for most of December and forecasts crude and condensate production will slip to 950,000 bpd this month from 1.1 million bpd in December, Livia Gallarati of Energy Aspects said.
Output in Iraq and the UAE was little changed. Estimates for these nations vary widely, with many outside sources putting the countries' output higher than the countries themselves.
While the Reuters survey and data provided by OPEC's secondary sources show they are pumping close to the quotas, other estimates, such as those of the International Energy Agency, say they are pumping significantly higher volumes.
The Reuters survey aims to track supply to the market and is based on flow data from financial group LSEG, information from other companies that track flows, such as Kpler, and information provided by sources at oil companies, OPEC and consultants.
(Reuters, January 9, 2026)